Electric horn or other acoustic signal producer



M GREINER Dec. 12, 1933.

ELECTRIC HORN OR OTHER ACOUSTIC SIGNAL PRODUCER Filed April 24, 1928 2Sheets-Sheet l Dec. 12, 1933 GRElNER 1,939,347

ELECTRIC HORN OR OTHER ACOUSTIC SIGNAL PRODUCER Filed April 24, 1928 2Sheets-Sheet 2 Jrzuenfor" MAX GREINEK Patented Dec. 12, 1933 ,PATENTOFFICE ELECTRIC HORN OR OTHER ACOUSTIC SIGNAL PRODUCER Max Greiner,Berlin-Charlottenburg, Germany Application April 24, 1928, Serial No.272,448, and in Germany October 11, 1926 7 Claims.

My invention relates to electric horns for producing acoustic signals,and is primarily designed for use 'as an attachment for automobilesalthough it is applicable for other purposes.-

One object of my invention is a horn producing a clear tone resemblingthat of a trumpet. Another object is to provide a horn which is veryeconomical in consumption of electric energy and which is of extremelysimple and reliable construction guaranteeing a long life and negligiblewear. From another aspect my invention relates to a diaphragm which whenproperly mounted is subjected to a radial tensionlike a strained drumskin and is, therefore, particularly adapted for use in instruments forproducing acoustic effects.

Oiher objects and features of novelty will appear from the descriptionhereinafter and will be pointed'out in the claims.

In the accompanying drawings I have illustrated some embodiments of myinvention.

Fig. 1 represents an elevation of an electric horn, partly in sectionalong the line l1 of Fig. 2,

Fig. 2 is a section partly along the line 2-2 of Fig. 1,

Fig. 3 is a plan-view of the embodiment shown in Fig. 1, the cap beingomitted,

Fig. 4 is a perspective showing of the diaphragm in relaxed condition,

Fig. 5 illustrates a section along the line 5'-5 of Fig. 4,

Fig. 6 is a circumferential section of the diaphragm shown in Fig. 4,

Fig. 7 is an axial section corresponding to of Fig. 1 through a modifiedembodiment.

Referring to Figs. 1 and 2, 10 indicates a funnel for conductingand-collecting the acoustic waves generated by an oscillating diaphragm12 which closes one end thereof. While the funnel may be of any desiredshape, its interior is preferably unobstructed and free from any platesor other members which are capable of oscillating and causing adisturbance of the oscillations of the air body contained in the funnel.In this respect the invention may be diiferent from certain knownconstructions and, as a consequence, may result in a much clearer tone.To one rim of the funnel a cup-shaped flange 11 is'aftached in anysuitable manner and formed'to accommodate the diaphragm 12. A ring 13 isimposed upon the diaphragm and connected with the flange 11, forinstance hy means of rivets 14, clamping the rim of the diaphragm 12against the flange: A bail 15 that is placed upon the ring 13 invertical position, its

ends being fastened to said ring, preferably by means of some of therivets 14, (see Fig. 3). Over the straight top section of the ball aUshaped sheet-metal-piece 16 is slipped, which carries between l'lSdownwardly projecting arms an iron core 17 which is fixed in place bymeans of rivets 18. The iron core is formed with two downwardlyprojecting ends 19 provided with electro-magnetic coils 20 which arethus positioned in register with a diameter line of the diaphragm. Thewhole structure is covered by a cap 22 inserted inthe upwardlyprojecting margin portion of the flange 11. In the centre of the capalhole is provided through which a bolt 21 fixed to the bail 15 isprojecting. A nut 23 screwed upon the bolt 21 serves lo keep the cap 22in place. In the centre of the diaphragm 12 a hole is provided in whicha vertical bolt or pin 24 is inserted. This pin has a collar 25 bearingagainst the upper surface of the diaphragm and carries at its ends a nut26 screwed against the lower surface of the diaphragm. In this manner acomparatively rigid connection between pin 24 and the diaphragm isprovided which, however, cannot completely prevent a relative movementof the parts during the oscillation of the diaphragm. In order todiminish thedestructive effect of the resulting friction washers 2'1 ofa different metal, for instance of bronze, are placed between thediaphragm 12 and the shoulder 25 or the nut 26, respectively.

The upwardly projecting end of the bolt 24 car-- ries an armature 28attached in any suitable manner. In the embodiment shown, the upper endof the bolt 24 is of smaller diameter and the armature 28 is providedwith a hole to be slipped over said end. Beneath the armature 28 twowashers 29 are placed upon the bolt or pin 24 holding between them aspring-blade 30 which is thus rigidly connected with the bolt 24 inparallel relation to the diaphragm. The one end of this blade 30 isclamped between a bracket 32 and a clamping-plate 31 riveted thereto.The bracket 32 is carried by the ring 13' and secured thereto, forinstance by some of the rivets 14.

From the foregoing description it will be apparent that the blade 30 isarranged to participate in any oscillation which the diaphragmmayperform andthat, consequently, it increases the force with which thediaphragm counter-acts any axial displacement of the pin 24.

Another spring-blade 33. which is in the embodiment shown is integral"with the spring-blade 30 is attached to the pin 24, extending from theupper-end of the same parallel to the diaphragm. Its free end isweighted by means of two plates button switch 41 is pressed down.

34 riveted to the spring as shown in Fig. 1. A strip 35 of bronze isfolded over the end of the spring 33 and its ends are clamped betweenthe spring and the'plates 34. The floating weight 34 and the springblade are so dimensioned as to constitute an oscillating system having anatural frequency which is substantially lower than that of theoscillating system constituted by the diaphragm 12, the spring blade 30,the armature 28, the pin 24 and the parts rigidly connected therewith.In the embodiment shown, for instance, natural frequency of theauxiliary oscillating system formed by the floating weight andits-spring amounts to about fifty oscillations per second, while thenatural frequency of the main system amounts to about two hundred andfifty oscillations per second.

The electric circuit of the coils 20 diagrammatically indicated in Fig.2 is controlled by an automatic interrupter operatively connected to theoscillating system constituted by the diaphragm 12 and its associatedparts. The switch of the interrupter is molmted upon an arm 36 inwardlyprojecting from the ring 13. Separated and individually isolated byinterposed insulating pieces 37 are arranged two contact springs 38 and42 which are placed upon the arm 36 and attached thereto by means ofscrews 39. Contact studs 40 are provided on the freely projecting endsof these springs registering with each other so that a circuit from thebattery A may be closed through the coils 20, provided that the springThe upper spring 38 projects into the path of the spring 33 and is sobent that it tends to assume a position which is higher than thatillustrated in Figs. 1 and 2, and in which the contacts 40 areseparated. Also, the spring 42 has the tendency to raise to a a higherposition than shown so that, upon an upward movement of the upper spring38, it'will follow the same until it abuts against a stop pin 43. Thisstop pin is adjustably screwed into the projecting end of asheet-metal-arm 44' arranged in insulated position upon the insulatingpieces 37 and projects through a hole provided in the spring 38 withoutcontacting the latter. An abutment formed by a rivet 44 is secured tothe spring 33 in register with the spring 38 for engaging the same.Suitable washers of insulating material are inserted between the spring33 and the upper and lower head of the rivet 44 to insulate the lat ter.

In order to prevent an excessive oscillation of the system constitutedby the floating weight 34 and its spring a damping device is providedfor the same comprising'an angular spring 45 attached to the ring 13 andbearing with its upright arm against the end of the spring with a slightpressure. The support for the electric horn is preferably resilient, andelastic sothat the structure supporting the electro-magnet and the rimof the diaphragm is capable of oscillating in the same direction as doesthe oscillating system of the armature. In the embodiment shown thesupport is formed by two spring-blades 46 riveted to the lower surfaceof the flange 11 and connected to a bracket 47 by means ofa bolt 48. Thebracket 47 is fixed in the place where the horn is to be attached. Owingto this suspension the entire supporting structure is capable ofoscillating in a direction parallel to the oscillation of the diaphragm12.

While any suitable diaphragm may be used in connection with theafore-described construction I prefer a particular form embodying ceristhe case-when properly mounted in the hornf In relaxed condition thediaphragm assumes a form in which any circumferential section, inclusivea section along the ridges 51 for instance, represents a wave line suchas shown in Fig. 6. In the embodiment shown this wave line comprises twocomplete waves only, corresponding to the saddle shaped curvature of thediaphragm illustrated in Fig. 4.

In order to produce this curvature the ridges 51 are stamped in theordinary way in a flat and plane circular piece of particularly hardspring sheet metal. In the course of the stamping process interiorstresses are produced in the margin portions of the plate which causethe same when relieved to assume the peculiar shape. I have found that asatisfactory diaphragm such as illustrated may be produced from a plateof 4%," diameter and .008" thickness, the material being hardenedSwedish steel. If ridges such as illustrated are impressed to a depth of.05 a shape such as shown willresult. If deeper impressions are made ashape is obtained in which a circumferential section comprises more thantwo complete waves.

In the same manner as a wave line is increased in length when it isstretched to a straight line, the circumferential zone of the diaphragmis lengthened when the rim of the latter is clamped between planesurfaces. An increase in length of the circumference results, of course,in an increase in diameter whereby the central part of the diaphragm isstrained like a drum skin. In this condition the diaphragm resists witha strong forces any axial displacement of its center which is necessaryfor obtaining a high frequency anda clear tone, and thus constituting afloating weight. The force may be increased to a certain extent byaction of the spring 30.

The operation of the electric horn is as follows: When the button switch41 is pressed down while the various parts are at rest in the relativeposition shown in the drawings, the electromagnets 20 are energized andattract the armature 28. The spring 33, consequently, is raised and thefree ends of the contact springs 38 and 42 partake in this movementuntil the lower spring 42 abuts against the stop pin 43 whereby thecontact studs 40 are separated. Now the circuit previously establishedthrough the coils 20 is interrupted so that the latter are deenergizedand no longer attract the armature 28. Owing to the force exerted uponthe latter by the'diaphragm and the spring 30 which have beenbent, it isvehemently returned into the original position and, therefore, does notcome to rest when reaching the same but owing to the enertia imparted bythe combined action of the diaphragm and the spring 30 it continues itsmovement for some time until finally it is again returned. During a partof the return stroke towards the electromagnet the armature is attractedand its speed is consequently increased, hence, also, its amplitude ofoscillation. Owing to the special type of diaphragm as describedhereinbefore which has the feature of a stillness increasing with theamplitude of oscillation the frequencyof oscillation too is rapidlygrowing during the first stages of starting. After a short time of thisstarting period the auxiliary oscillating system constituted by thespring 33 and its weights 34 will be aided to pass through resonance bythe main armature system due to the higher frequency of the latter whichis impressed on the system 33, 34.

For easily overcoming this point of resonance and avoiding excessiveoscillation of the auxiliary system a clamping device is provided.

After passing through resonance the stiffness of the system 33, 34 addsto that of the armature system so that the latter reaches a finalfrequency which is higher than it would be due to the stiffness of thediaphragm 12 and spring 30 alone.

While in the embodiment shown the armature- 28 with the pin 24 forms themass of the oscillating system, any other mass or weight could be usedprovided that other suitable means for imparting the oscillation weresubstituted for the armature. It is an essential advantage, however,that the system is arranged for free oscillation, i. e. that it does notabut against any unresilient stop or contact which would prevent theoscillation from being gradually built up to the desired maximum. Forthis reason the contact members 38 and 42 are formed by resilientblades.

In order to produce a sufficiently strong sound the amplitude of theoscillating system must be comparatively large, about .15 for instance,in case of the afore-described diaphragm. On the other hand. the forcewith which the oscillating system resists its displacement must be highin low frequency. In the initial stages of the start-- ing period thespring 33 moves bo'dily together with the system of the armature 28 ashereinbefore stated. When the point of resonance ispassed, however, theweight 34 is unable to follow the quick movements of the armature buttends to remain stationary, and this the more strongly the higher thefrequency of the armature rises. The weighted end of the spring 33finally remains nearly stationary so that the spring 33 exerts the sameeffect upon the armature as does the spring 30, i. e. it increases thestiffness of the oscillating system.

As this effect does nottake place until a high frequency has alreadybeen reached it avoids the afore-mentioned disadvantages which wouldresult from an invariable stiflness of the system; Consequently, a hightrumpet-like tone can be obtained.

A particular advantage results from the coordination of the interrupterswitch 40 with the oscillating system formed by the weighted spring 33.As the free end of the latter has a small amplitude, the contacts 40 arenot opened until the armature has nearly reached the upper end of itsstroke. This results in a particular economical electric currentconsumption which is still further decreased by the elastic suspensionof the entire supporting structure for the electromagnet. Thissuspension renders the electro magnet capable of oscillating contrary tothe oscillation of the armature. The relative movement between thearmature and the electromagnet, however, counts for the intensity of thesound produced and this movement is the total of the individualoscillations of the armature and of the electromagnet.

In the embodiment shown in Fig. '7 similar reference numerals indicatecorresponding parts. The diaphragm 130 is clamped between the flange 111and the ring 113 and provided with an armature 128, the circuit of whichis controlled by the interrupter-switch 140 diagrammatically indicatedin the drawing. The armature 128 carries a spring blade 133 provided atits ends with weights 134. The latter are so dimensioned with respect tothe spring 133 that the frequency of their natural oscillation is asmall part of the frequency of the system formed by the diaphragm 130with the mass 123. When referring to the frequency of the naturaloscillation or, briefly, to the natural frequency of the systemconstituted by the diaphragm and the armature, or the weighted springblade, respectively. I wish to of a free oscillation. Similarly, thenatural frequency of the system 12, 28 would be obtained if the weightedspring 33 were cut off. Spring blades 145 serve to damp the oscillationof the system with low frequency.

As the operation of this embodiment equals substantially that of thefirst described embodiment a detailed description thereof may be.dispensed with herein.

The two end positions between which, the spring blade 133 is oscillatingduring the normal operation are indicated in dotted lines clearlyshowing that the weights 134 remain nearly stationary whereby thestiffness of the oscillating system is increased to an extent necessaryfor producing. a high trumpet-like sound.

What I claim is:

1. In an electric horn the combination comprising a diaphragm, anarmature rigidly attached to the central part thereof to form therewitha main oscillating system, electromagnetic means to impart oscillationsto said armature and diaphragm, a spring blade attached to and carriedby said armature, a mass on the free end of said spring'bladeconstituting therewith an auxiliary oscillating system, the mass and thespring blade being so dimensioned that the natural frequency of saidauxiliary system is materially lower than that of said main system,whereby said spring will increase the eifective stiffness of said mainsystem at normal operation without increasing the stiffness at theinitial actuation.

2. In an electric horn the combination comprising a diaphragm, anarmature rigidly attached to the central part thereof to form therewitha main oscillating system, electromagnetic means to impart oscillationsto said armature and diaphragm, a spring blade attached toand carried bysaid armature, a mass on the free end of said spring blade constitutingtherewith an auxiliary oscillating system, the mass and the spring bladebeing so dimensioned that the natu ral frequency of said auxiliarysystem is materially lower than that of said main system, whereby saidspring will increase the effective stiffness of said main system atnormal operation without increasing the stiffness atthe initialactuation,

and damping means coordinated with said spring blade to dampen theoscillation of said auxiliary system.

3. An electric horn comprising a diaphragm, a support therefor, anarmature rigidly attached to the central part of the diaphragm to formtherewith a main oscillating system, an electromagnet carried by saidsupport to impart oscilla tions to said armatureand diaphragm, a spring.

blade attached to and exclusively carried by said armature, a weightcarried by said spring blade and forming therewith an auxiliaryoscillating system, said weight being so dimensioned with regard to thespring blade that the natural frequency of said auxiliary system ismaterially lower than that of said main system, whereby said springwill'increase the effective stiffness of said main system at normaloperation without increasing the stiffness at the initial actuation.

.4. An electric horn comprising a funnel, a diaphragm of spring sheetmetal closingone end of said funnel, the interiorof said funnel beingunobstructed, an armature rigidly secured to the central part of saiddiaphragm forming with the latter a freely oscillating system, anelectromagnet rigid with respect to said funnel for attracting saidarmature, an'electric interrupter switch in circuitwith saidelectromagnet, a spring blade connected with said armature in parallelrelation to said diaphragm, said spring blade having its one endattached in fixed relation to said funnel and its other end freelyprojecting beyond said armature, a weight fastened to the free end ofsaid spring blade, said weight being so dimena sioned with respect tosaid freely projecting end that the'frequencymf its natural oscillationis substantially lower than that of said system whereby said spring willincrease the effective stiffness of said main system at normal operationwithout increasing the stiffness at the initial actuation, the contactsof said switch being positioned for actuation by the movement of thespring blade. I

5. The combination set forth in claim 7 provided with damping meanscoordinated with said spring to damp the oscillation thereof.

6. An electric horn comprising a funnel, a diaphragm of spring sheetmetal completely closing the one end thereof, an armature rigidlysecured on the central part of said diaphragm forming with the latter afreely oscillating system, an electromagnet rigid with respect to saidfunnel for actuating said armature and diaphragm, a spring bladeconnected with said armature in parallel relation to said diaphragm,said spring blade having one end attached in fixed relation with respectto said funnel and its other end freely projecting beyond said armature,a mass fastened to said free end, the weight and position of said masswith respect to said freely projecting end being such that the frequencyof its natural oscillation is substantially lower than that of saidsystem whereby said spring will increase the effective stiffness of saidmain system at normal operation without increasing the stiffness at theinitial actuation,- two superimposed contact spring blades forming partof the circuit of said electromagnet and arranged between said diaphragmand said first mentioned spring blade, normally bearing against eachother and against said spring blade and tending to separate when thelatter is lifted, and an adjustable stop arranged to limit the movementof the lower contact-spring blade towards the, upper contactspringblade.

'7. In an acoustic signal producer, the combination comprising anelectric interrupter including an oscillatory armature and a contactcooperatively connected therewith, a diapragm of springsheet metalhaving a central portion directly carrying said armature and surroundedby a circular ridge and being so shaped in relaxed condition that acircumferential section along said ridge forms a wave-line, a supporthaving an annular surface, means to press the marginal portion of saiddiaphragm against said surface to produce a tensional condition in saiddiaphragm which will increase the effective stiffness of the diaphragmat normal amplitudes of oscillation without increasing in proportion thestiffness at the amplitude requisite forthe initial actuation of saidcontact, and an electromagnet secured to said support-for impartingoscillations to said armature, the latter forming an oscillating systemwith said diaphragm, a floating weight, and a spring substantiallyparallel to the diaphragm and connecting said armature with saidfloating weight, whereby the weight may oscillate perpendicularly tosaid diaphragm, the said weight being so dimensioned with respect tosaid spring that its natural frequency of oscillation is considerablyless than that of the oscillation of said system whereby said springwill increase the effective stiffness of said system at normal operationwithout increasing the stiffness at said initial actuation.

MAX GREINER.

